Process for the manufacture of refractory materials and resultant product



3,679,266 MANUFACTURE OF REFRAC- AND RESULTANT PRGDUCT Grenoble, France, assignor to Pechiney, Compagnie de Produits (Ihirniques et Electroinetel- PRSCESS FGR TEE TORY MATERIALS Andre Galy,

lurgiques, Parts, France, a corporation of France No Drawing. Filed July 7, 1959, Ser. No. 825,409

Claims priority, application France July 18, 1958 Claims. (Cl. 106-56) The present invention, which is the result of applicants researches, relates to a new refractory and insulating material and, more particularly, to a process for the manufacture of carbon refractory and insulating matenals.

It is already known to classify refractory materials according to their chemical composition into ((1) Acid products, among which are included clay and siliceous, etc. compounds;

(/2) Basic products, which include magnesia, dolomite, zirconia, etc.

(c) Amphoteric corundum; and lastly (d) Neutral substances, such as carbon and chromite.

It is known, for example, to make refractories having an amorphous or graphitic carbon base by with bituminous or tar derivatives.

It is also known that the basic characteristics of every refractory material are its porosity, pyroscopic resistance, mechanical strength, chemical corrosion, etc.

Lastly, it is known that the refractory materials play a primary role in the technology of furnaces and metallurgical apparatus.

' However, to applicants knowledge, there does not exist at present any refractory or insulating material capable of withstanding temperatures equal to or higher than 1800 C., or even 1500 C., in the presence of carbon and under a vacuum.

The present invention has for its object a refractory and, moreover, an insulating material capable of withstanding without damage temperatures higher than 1800 C. at normal pressure, or 1500 C. under a vacuum in a reducing or neutral atmosphere. The material of the present invention is constituted of pure porous carbon.

substances, such as bauxites and mixing clays facturing such a product and its applications.

The other objects of the invention will be disclosed in the course of the following description.

Applicant has discovered a new outstanding pyroscopic and chemical re sistance, the following remarkable characteristics: low density, below 0.4 and close to 0.25; low thermal conductivity, of the order few tenths of a kilocalory per square meter of surface, per meter thickness, per dea thermal conthan kg./cm. and, finally, easy workability and application, as it can be machined by simple tools suitable for wood and converted to any desired shape.

Applicants researches have established that the said product can be obtained by heating to high temperatures, above 400 C., and preferably of the order of 1200 C. and higher, a mixture of solid compounds having a carbohydrate base, such as oses, holosides, heterosides, cellulose, etc., and having a carbohydrate base, such as oses, holosides, heterosides, polyosides such as cellulose, stare vegetable gums (gum of wood, gum arabic, gum of cherry wood) etc. and/or proteins, such as gelatins, glues.

Applicant has also developed a process for the 37Jdh Patented Feb. 26, 1963 fie limitation, starch, 1 glue, etc., or of mixtures of such compounds. suspension, there is added an amount compounds such as, and without derivatives, for example,

T0 :thlS of porous solid limitation, cellulose wood chips, straw, cellulose sponge, etc, flours, edible pastes, etc. There is obtained in this Way, a pasty mixture which is very viscous at the mixing temperature and which tends to solidify on cooling to room temperature.

The mixture, constituted of a porous solid skeleton gel-forming progressively raised preferably C. Such heating can be atmosphere. invention, the temperature is per hour and, hour.

The constituents of the mixture are then totally coked and the refractory and insulating elements obtained in this manner are progressively cooled.

However, if the maximum heating temperature has been only of the order of 1200 C. then, there still remains in the elements, besides carbon, a small quantityof the order of a few percent-of alkaline ashes originating from the starting products. In order to remove these ashes completely, it is necessary to raise the temperature of the elements above 1200 C. and preferably, in the neighborhood of 1700 to 1800 C.

According to a preferred embodiment of the invention, the elements are allowed to cool progressively and slowly from about 1200 C.which is the temperature attained in the course of first heating-to a temperature below 400 or 300 again heated, under vacuum, to a temperature of the order of 1700-l800 C. This second treatment has for its purpose first, to remove the ashes and, strength of the elements.

The following examples, which are in no way given by way of limitation, will illustrate the process for obtaining the refractory and insulating material of the present invention.

raised a few tens degrees more particularly, about 20 degrees per Example 1 In a mixer provided with a heating device and fitted with temperature controls, there are introduced 200 liters (of the order of 250 kg.) beet sugar molasses containing about 50% water. Mixing is effected for one half hour at 120 C.; the evaporated water amounts to about 50% of the initial water content.

There is then introduced kg. chips, for example, of a resinous wood, produced by a planer and which have been preliminarily screened on 5 to 20 mm. sieves in order to retain only chips of a size between these two dimensions. The mixture of chips and molasses is stirred in the same manner for one hali.. hourl at 120 C.

There is then obtained a very viscous'paste which becomes almost solid if it be again allowed: to attain room About 50 shells (pipes) are filled in this and are then piled up in the trucks oi.a tunnel iurnace oi the Protection against L the heating ceramiceiurnace type. gases is secured by means ofa layerlot powderedc silica sand placed on the upper part1; v

The temperature is raised about 20, degrees per'j h'ou until it reaches 1100 to 1200 C.; coolih'gjis gthen' car ried out at the same slow rateuntil a temperature (if-300 C. or below is reached. p p The bricks obtained in this way are thengsdbmi to a second treatment at a high vacuum, p in the neighborhood of 1800 C. These' bric cs', possess a volume of the orderof 150 lit ers after the heating, lose during this second heat. .treatment;;5i to of their weight Without any substantia ume. The bricks finally produced possess thejfollowing ha'r acteristics'. v V Thermal conductivity--. About 0.5 kcaL/mFYmJ f (1/11.; Specific gravity About 0.25 1 Compressive strength About to 12 kg./cm. Ashes; 0.2%.

These bricks are easily cut and shaped with t fe usual.- tools for wood. They can be used as refractory, and in sulating materials in the constructionfof industrial tur-' naces, and/ or any metallurgicaliequipment orjth'e like,

which require the use of relractory'or insulating prod= ucts capable of withstanding temperatures higher than 1800" C. at normal pressure in a neutral or reducing atmosphere, for example, in the presence of carbon;

moreover, they are quite-adapted for work under a high vacuum and'at temperatures higher than 1500 C.

Example '2 A manioc meal slurry is prepared by boiling a sus-, pension of 10 kg. meal in 100 liters Water. This slurry is introduced into a mixer in which there is also added 100 kg. (that is, about.250 liters) edible pastes of the commercial type, in the form of grooved cylinders having roughly, the following dimensions: a diameter of 12-15 mm, a length of 50 mm; V

, The'mixture is stirred for about to minutes at a temperature of the order of 40 to 60 C. i The resultant paste is then poured into sheet iron molds having the following dimensions: 33 X 17 X 9 cm. The paste is slightly tamped therein under a pressure of about 100 to 200 .g./cm. The'molds containing the paste are introduced into an electrically heated tunnel-furnace, the V temperature of its hottest section being controlled to 400 C. By the use or a mechanical conveyor belt, the inoldsadvance in the furnace. at a rate corresponding to a rise in temperature of 20 to 25 degrees C. per hour. The temperature of 400 C. is high enough to insure the col ing of the mixture, and is low enough to permit sweeping of the furnace by .a current of air which assists in the removal of water and hydrocarbon vapors, liberated from the bricks, without inducing combustion.

After cooling at the same rate as they. wereheated', the bricks almost attain their final shape. Their volume has been reduced about 50%. The dimensionsiare those of standard bricks, 22 x 11 X 6 cm. i

Nevertheless, these bricks have still retained some heavy tars and the total amount of alkaline ashes contained in the initial products,

change in 51;

e'i rlsi e r They are then submitted to a second treatment which raises their temperature to 1800 C. under a high ,vacu-- During this treatment, they are converted to pure ,"d'privedofi ashes, and lose 4% to 5% of their 5 weight.

,The. character istics of the refractory and insulating 1 bricks obtained inthis manner are substantially identical with those oflthejbricks' obtained according to Example 1. Ar'n'ong "thetrionaoitidizing, i.e. reducing or neutral, at- 'mospheifes whichcan be used for carrying out the first heat treatment according to the present invention, are for unstance neutral atmospheres such as rare gas: argon,v ellum ornitrogen or-reducing atmospheres such as: car--' be mono ride hydrogenyor methane, natural gas, crack- 1 in-gf gaslar'nrnoniac. v i

The secorid heat'treatrnenteto rernove ashes and heavy -t'ars-'-isl carried out in a vacuum which may vary between "l micronand 10-millirneters ot mercury; The termholosides as used in the present specifica- 1:20 .tion refer for instance to 'saccharose, lactose, maltose.

The termfheterosides refer to natural extracts such .as: tanin, salicin, amygdalin. s Thelterm: -oses refer to natural; sugars such as: glucos'e, mannose, galactose, fructose.

1? Process for making refractory heat insulating product consisting substantially of carbon comprising the steps of: intimately mixing, at a temperature of about 100 C.,

7 particles ofa porous solid substance consisting substantially era compound selected from the group consisting of oses, holosides, heterosides, and polyosides, with a liquid binder capable of forming a'gel consisting substant-ially of an aqueous suspension-of a material selected from-. the group consisting of oses, holosides, heterosides, polyosides, gelatine, and glues, to form a pasty mixture at vthemixing temperature of a porous solid skeleton thor- :oughlyimpregnated with the gel-forming binder; placing thispasty mixture into molds corresponding to the shape of the desiredrefractory product; submitting this paste to a slightpressure of about l00-200 grams/cm. to thereby iiisurethe-uniform filling ofthe entire mold without substantially increasing the bulkdensity of the mass; heating the mixture progressively in anon-oxidizing atmosphere up to a temperature of about 1200 C. whereby the pasty mixture is coked and transformed into carbon.

2." A process according to claim 1, wherein said product is subsequently progressively heated in a vacuum to a temperature range between about 1200 C. and about ratio 0.

3. A process according to claim 1, wherein the heating is carried outprogressively soas to raise the temperature oi the paste at the rate of 'about' 20 C. per hour.

4. A process according to claim 1, wherein the product 55 isco'oled to about 300 C. and subsequently progressively heated to a temperature up to 1800 C. l

5. A process according to claim 1, 'wherein'the product is progressively cooled to about 300 C. at the rate of about 20*. (3.. per hour, and subsequently progressively heated to atemperature up to 1800? C.

6. A refractory heat insulating product produced by the process of c1 7. A refra aim 1.

ctory heat insulating product produced by the process of claim 2.

References Cited in the file of this patent UNITED STATES PATENTS 

1. PROCESS FOR MAKING REFRACTORY HEAT INSULATING PRODUCT CONSISTING SUBSTANTIALLY OF CARBON COMPRISING THE STEPS OF: INTIMATELY MIXING, AT A TEMPERATURE OF ABOUT 100*C., PARTICLES OF A POROUS SOLID SUBSTANCE CONSISTING SUBSTANTIALLY OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF OSES, HOLOSIDES, HETEROSIDES, AND POLOYSIDES, WITH A LIQUID BINDER CAPABLE OF FORMING A GEL CONSISTING SUBSTANTIALLY OF AN AQUEOUS SUSPENSION OF A MATERIAL SELECTED FROM THE GROUP CONSISTING OF OSES, HOLOSIDES, HETEROSIDES, POLYOSIDES, GELATINE, AND GLUES, TO FORM A PASTY MIXTURE AT THE MIXING TEMPERATURE OF A POROUS SOLID SKELETON THOROUGHLY IMPREGNATED WITH THE GEL-FORMING BINDER; PLACING THIS PASTY MIXTURE INTO MOLDS CORRESPONDING TO THE SHAPE OF THE DESIRED REFRACTORY PRODUCT; SUBMITTING THIS PASTE TO A SLIGHT PRESSURE OF ABOUT 100-200 GRAMS/CM.2 TO THEREBY INSURE THE UNIFORM FILLING OF THE ENTIRE MOLD WITHOUT SUBSTANTIALLY INCREASING THE BULK DENSITY OF THE MASS; HEATING THE MIXTURE PROGRESSIVELY IN A NON-OXIDIZING ATMOSPHERE UP TO A TEMPERATURE OF ABOUT 1200*C. WHEREBY THE PASTY MIXTURE IS COKED AND TRANSFORMED INTO CARBON. 